There are numerous patents on grafting maleic anhydride and other monomers to polyolefins. For example U.S. Pat. No. 4,612,155 of R. A. Zelonka and C. S. Wong teaches the grafting of unsaturated monomers onto the polyolefins in an extruder.
U.S. Pat. No. 3,862,265 and its division No. 4,001,172, both issued to Steinkamp et al, disclose an extrusion reaction of polyolefins to a high level of grafting having melt flow rates (MFR) when measured at 230.degree. C. that are claimed to be up to 1000 dg/min but for polypropylene (PP) only up to 71 dg/min. The percent of maleic anhydride grafted to PP is shown to be only up to 0.53% by weight. These patents show that the use of a special reaction zone within an extruder can be chosen to effect intensive mixing of added reactants to a polymer or distribution of the added reactants to a polymer. The process allows not only the polymer to be modified in terms of its rheology but it may also be simultaneously modified by chemical means.
British Patent No. 679,562 shows graft polymerization of polymers when subjected to suitable mechanical mixing through filters or capillary tubes at high linear velocities.
U.S. Pat. Nos. 3,177,270 and 3,177,269 each discloses the formation of a graft copolymer by adding a monomer and an initiator. The products are "malaxed" to such a low degree that no degradation takes place.
U.S. Pat. No. 3,013,003 shows that degradation in an extruder can be controlled by utilizing a stabilizer.
The patents noted above do not disclose the art of producing a material having a melt flow rate (MFR) above 500 dg/min in an extruder or a material that is pelletizable, or a highly-grafted material. Some of the previous patents state total amounts, not actual grafted amounts of monomer in a polyolefin product.